1. Field of the Invention
The present invention relates to such an antenna device for vehicles that can be made available by installing an antenna assembly in a door mirror case of a vehicle.
2. Description of the Related Art
Radio and TV tuners have so far been mounted on vehicles. In addition, an increasing number of mobile telephone and/or data processing terminals and global positioning systems (GPSs) applied to car navigation systems have been mounted on vehicles.
Receiving radio waves is essential to the use of such equipments on vehicles and necessitates antenna provision. Because the wider the field of view of an antenna, more easily the performance of the antenna will be assured, it is ideal that an antenna protrudes from the car body after installed from only the point of view of antenna performance. However, the antenna protruding from the car body has also demerits, such as causing a bottleneck in car design and wind noise during drives. That is why car designers and users prefer antennas that do not protrude from the car body if possible to those protruding.
As one type of antennas that do not protrude from the car body, glass antennas have been used to provide an antenna pattern arranged on the surface of the rear window glass. One problem of glass antennas is that they are liable to be affected by the variation in specific inductive capacity of the window glass and thus managing the production process is difficult. Another problem has been proposed that arranging many lines of an antenna pattern in an area on the glass limits the field of view of the driver.
Another possible location where such antennas can be provided is the inside of on the rearview mirror assembly or the outside mirror (door mirror) assembly. Installing such antennas in these locations completely eliminates the problem of external appearance. Japanese Patent Laid-Open Publication No. Sho 63-170349 proposed the antenna provision arranged on the inside of the rearview mirror assembly and the outside mirror assembly.
If an antenna is arranged on the inside of the door mirror assembly, its size must be small. In order to reduce the size of an antenna for receiving TV broadcasting carriers, which is referred to as a TV antenna hereinafter, it is suitable to make it a belt shape rather than a linear shape. However, the door mirror can be turned to the close position and it is generally thought that a belt-shaped antenna is hard to retain its shape when in the close position.
As regards an antenna for receiving GPS carriers, which is referred to as a GPS antenna hereinafter, it is relatively easy to reduce the size of the antenna assembly. Thus, it is thought that a GPS antenna can be housed in the door mirror assembly in the physical (dimensional) aspect. However, if the size of a GPS antenna assembly is reduced, its antenna receiving performance may often be likely to degrade significantly and the decrease in the production yield is anticipated. That is why no proposal has so far been made to house a GPS antenna in the door mirror assembly. In addition, such GPS antennas have to be protected from the adverse effect caused by radio waves reflected by roads.